This invention relates to a communication device connected to a network, a communication system, and a communication control method. More specifically, the technique relates to a session control device and a communication access control method, in particular, a session control device in a communication system to which Session Initiation Protocol (SIP) is applied and an application control method in a communication system to which an application server device is applied.
Third-generation mobile communication systems aim for quicker and better access to text, audio, video, and other various multimedia services. At present, the 3rd Generation Partnership Project (3GPP), and the 3rd Generation Partnership Project 2 (3GPP2) are working toward standardization of “All-IP-based mobile communication network” in order to provide, over packet switched networks, multimedia services that make use of an Internet Protocol (IP) technology. An all-IP-based mobile communication network is called an IP multimedia subsystem (IMS) in 3GPP, and a multimedia domain (MMD) in 3GPP2.
In an IP multimedia subsystem (IMS), a function named Call Session Control Function (CSCF) executes All-IP network session control, and a server called Home Subscriber Server (HSS) keeps subscriber information. An application is provided in the IMS by an application server (AS).
There are roughly three types of CSCF classified by their roles, P-CSCF, I-CSCF, and S-CSCF. P-CSCF, which stands for Proxy-CSCF, is a CSCF that is accessed by a mobile terminal first. I-CSCF, which stands for Interrogating-CSCF, identifies which S-CSCF is assigned to the mobile terminal. S-CSCF, which stands for Serving-CSCF, is placed in a home network to control and manage the session state (see, for example, “3GPP2 X.S0013-002-A v1.0, All-IP Core Network Multimedia Domain §4.6”, December 2005, retrieved on May 29, 2006 from the Internet, page URL: <http://www[dot]3gpp2[dot]org/Public_html/specs/X.S0013-002-A_v1.0—051103.pdf>)(“[dot]”=“.”).
Session Initiation Protocol (SIP) is employed as a session control protocol (see, for example, IETF RFC3261, “SIP: Session Initiation Protocol §4”, June 2006, retrieved on May 29, 2006 from the Internet: <URL: http://www[dot]ietf[dot]org/rfc/rfc3261.txt?number=3261>)(“[dot]”=“.”). SIP is a protocol specified by IETF to control IP multimedia communication sessions. A typical example of services that use SIP is Voice over IP (VoIP). VoIP is a technology for transmission and reception of audio information over IP networks. In VoIP communications according to SIP, a virtual communication path (session) is set between communication devices before a communication is started. Audio data is transferred in the form of IP packets along the set communication path. SIP controls establishment, maintenance, and disconnection of a session between communication devices in VoIP communications.
Media information such as attributes of audio data is determined at the time a session is established. A communication device notifies media information following Session Description Protocol (SDP) which is contained in an SIP message. According to SDP, various kinds of session-related information (e.g., IP address, port number, and media type) can be described.
IMS presents roughly two types of AS activation methods. One is to use a service activation condition contained in subscriber information, and the other is to use Public Service Identity (PSI), in other words, application identifier. PSI is set beforehand in some cases, and is created dynamically in other cases.
The AS activation method that uses a service activation condition in subscriber information will be described first.
An HSS holds subscriber information (service profile) for each user authentication identifier. An S-CSCF obtains the subscriber information from the HSS upon location registration. Subscriber information of a user who subscribes to an application contains “Initial Filter Criteria”. The S-CSCF processes “Initial Filter Criteria” upon reception of the first SIP request, and judges whether to activate an AS.
The AS activation method that uses PSI will be described next.
Public Service Identity (PSI) is an identifier for identifying an application that is provided by an AS. PSI is used in order to identify a group that multiple users join, such as a forum.